Since its invention, the polymerase chain reaction (U.S. Pat. No. 4,683,202) has become a powerful force in biotechnology. It is a method to exponentially amplify essentially exact copies of a DNA segment. DNA is a double stranded molecule that when heated to temperatures such as 95° C., will dissociate into two separate strands. Using small synthetic DNA fragments called primers that can complementary base pair to the dissociated DNA strands at temperatures such as 45-65° C., the primers anneal to the template DNA. Finally, elongation takes place at around 72° C. using an enzyme called a DNA polymerase to extend off of one end of the primer by adding complementary nucleotides (dNTP's) to the extant original template DNA—making a new copy strand of DNA. Both of these two DNA strands are used in subsequent PCR cycles as templates along with the annealed primers to make two new copy strands of DNA for a total of four strands, which are called elongation events. By repeating the cycle of dissociating, annealing and elongating the reaction again, there is a doubling of new DNA strands produced. Repeat the cycle over 30 times and theoretically there are billions of exact DNA copies in the reaction vessel. These heating and cooling cycles, along with the template DNA, primers, dNTP's and DNA polymerase, are what constitute the PCR method. PCR is usually performed in automated devices that thermocycle the temperatures needed for the production of amplification products after all of the template DNA, primers, dNTP's and enzyme have been added to a sample vessel.
Conventional PCR devices, such as Peltier thermoelectric devices like the AB 9700 (U.S. Pat. No. 7,133,726 B1), convection heat exchangers like the Roche LightCycler (Wittwer, C. T., et al., Anal. Biochem. 186: p 328-331 (1990) and U.S. Pat. No. 5,455,175) and the like, are typically power hungry, take a while to complete a run, and/or are difficult to transport. All these PCR devices must thermal cycle in order to heat and cool the sample vessels they hold. The 9700 does this by constructing its sample holder out of a big block of metal and pumping heat energy into and out of the system through thermal conduction. Electrical energy is required both to add heat energy to the sample block and to remove heat energy from the block. This requires a lot of electrical energy due to the large mass of the sample block. For example, the AB 7500 consumes approximately 1,080 Watts during a run. The LightCycler avoids the large sample block by using thin capillary tubes with relatively small masses and cycles the temperature by convection with heated air. Like the 7500, the heating element in the LightCycler uses a lot of electrical energy.
Most of these devices are designed to be setup in a laboratory environment and not moved from location to location because they are large and heavy. Moving such devices typically requires a strong person, or a sturdy-wheeled vehicle such as a reinforced wagon or handcart. Further, it is common that these devices require a standard 120V to 250V outlet for power. Further, the devices cannot readily be moved from room to room once inside a laboratory. For standard PCR devices like the AB 7500, the run time for 40 cycles is 60 minutes. By trying to run them faster, you reduce the efficiency of the PCR reaction, which means that the sensitivity of the reaction is reduced. Portable and fast PCR devices are needed, especially in fields like medical diagnostics, where a physician needs test results in 15-20 minutes in a point of care (POC) situation. Additionally, the cost of these traditional PCR thermal cyclers limits their application to R&D, medical labs, forensic and other testing facilities. One market that is completely underserved due to cost, is education. A small, rapid, and low cost PCR device would allow high schools, small business labs, and smaller colleges the opportunity to finally perform testing and education that is currently cost prohibitive.
Prior art (Festoc, U.S. Pat. No. 6,821,771) described a heating plate having at least two zones for heating at two different temperatures. What this prior art failed to anticipate was the need to thermally isolate one heating element from another. By placing a higher temperature element in close proximity to a lower temperature element on a heating plate, a thermal gradient is created as described by Lurz (U.S. Pat. No. 6,767,512). The current disclosure solves this problem by adding sufficient insulating materials, which eliminates the thermal gradient and provides for proper thermal control for high efficiency biological reactions, such as PCR. Additionally, the prior art failed to anticipate the need for a cooling block to extract heat energy from a sample vessel when transitioning from a high temperature heating element to a lower temperature heating element. The current disclosure provides for a cooling block, which reduces the overall run time giving faster run results.